The objective of this study is the biochemical characterization of the role of cell surface receptors in coagulation and atherogenesis. This will include: 1) In vivo catabolism of Protease-Inhibitor complexes. The rapid clearance from blood of complexes of alpha 2 macroglobulin, alpha 1 antitrypsin and antithrombin III with proteases will be probed in mice utilizing competitive inhibition to determine the mechanism of clearance. The following will be evaluated: the reticuloendothelial system; hepatocyte and macrophage receptors for exposed galactose, N-acetylglucosamine, mannose and fucose; a receptor for clustered positive charges; a unique protease-inhibitor receptor(s). Moreover, circular dichroism and fluorescence spectroscopy will be performed to determine if conformational changes occur when protease-inhibitor complexes form. Such changes may explain why complexes but not free inhibitors clear rapidly. 2) Platelet Interactions, a possible role of cell surface carbohydrate receptors. A recent proposal that platelet aggregation requires a cell surface lectin will be studied utilizing both competitive inhibition of aggregation by glycoprotein derivatives and by glycosidase treatment of platelets prior to aggregation. Studies will also be performed to examine the role of platelet galactosyl transferase in aggregation utilizing alpha lactalbumin, which binds to galactosyl transferases, to determine if platelets exposed to alpha lactalbumin will still aggregate. The role of platelet glucosyl transferase in platelet adhesion to collagen will also be examined utilizing collagen bound to Sepharose together with competitive inhibitors of glucosyl transferase. 3) Platelet Smooth Muscle Growth Factor (SMGF) and its action on Vascular Smooth Muscle Cells (SMC). Platelet SMGF may be a mammalian mitogenic lectin. Therefore, studies will be performed to determine if addition of glycoprotein derivatives block the mitogenic action of SMGF on SMC. Glycosidase treatment of SMC will provide a second way of seeking a lectin-like reaction between these cells and SMGF. The kinetics of binding of growth factor to SMC will also be studied utilizing purified radiolabeled SMGF to determine if a receptor exists, its specificity, saturability and reversibility of binding.